1. Field of the Invention
This invention relates generally to medical diagnostic systems and methods. It relates particularly to a system and method for providing a probabilistic diagnosis of physiological dysfunction present in any of several tubular cavities within a living body.
2. Description of the Related Art
Motility within tubular structures of the body typically is the result of a complex interaction of muscles and their neural control mechanisms. Motility disorders that most commonly reach clinical significance are the motility disorders of the gastrointestinal tract. The prevalence of these disorders is significant, and their diagnosis and management consumes a large amount of health care resources. A variety of methods have been employed to correctly diagnose the nature of motor dysfunction, including radiological, radionuclide, and endoscopic procedures. However, these diagnostic tests only provide qualitative and often crude information ultimately used to establish a proper diagnosis of motor dysfunction. Their focus primarily is on evaluation of bolus transit or the luminal surface, excluding structural lesions that may produce clinical presentations mimicking motor disorders.
Intraluminal manometry is a very sensitive method of detecting motor dysfunction and has become the diagnostic gold standard in some parts of the gastrointestinal tract. Pressure measurements have the capability of determining fine errors in motor control before gross alterations in transit are apparent by other testing methods. Likewise, the quantitative outcomes of pressure measurements potentially can classify the type of dysmotility, even when the measured defect is minor. This can lead to earlier interventions and more appropriate treatments. Despite the appeal of intraluminal manometry, currently available systems have important limitations. The most important of these is that few recording sensors are used, the sensors are spaced such that spatial resolution is inadequate, and the resultant methods of analysis are inconsistent because of lack of sufficient data.
Intraluminal manometry is accomplished either by use of electromechanical systems with transduction (recording) devices embedded in intraluminal probes or water-perfused systems with the intraluminal catheter attached to extracorporeal transducers. In the former systems, current intraluminal probes typically include no more than 4 sensors, severely limiting the amount of acquired pressure information. For example, the esophagus, the most commonly studied gastrointestinal organ for its motor function, is more than 20 cm long within its body, and several centimeters of sphincter are found at each end. Best approximation of the peristaltic wave of motility requires sampling at 1-cm intervals. Consequently, the present devices are considerably inadequate. To completely characterize the peristaltic wave, from pharyngoesophageal region through the lower esophageal sphincter in all adult subjects, at least 30 sensors recording pressures simultaneously from an intraluminal probe are required. A system of this type presently is not available.
Commercial water-perfused systems are available with more recording sites than the electromechanical systems. The most advanced of these presently allows for 21 recording sites within a probe diameter tolerated by adult subjects for esophageal instrumentation. Consequently, even with this system, only a portion of the esophagus and one bordering sphincter can be studied simultaneously. Water-perfused systems with fewer recording sites are in common use because of their lesser expense than electromechanical devices. However, the demonstration of motor dysfunction is expectedly limited. Water-perfused systems also suffer the limitations imposed by their sensitivity to gravity bias and the important technical burdens in maintaining the perfused catheters and pneumohydraulic pump apparatus. The system requires meticulous cleaning and maintenance to provide accurate pressure data from repeated use, and the apparatus is cumbersome and poorly transportable.
The electromechanical systems generally employ a miniature silicon diaphragm which has a very limited circumferential extent, and which incorporates a piezo-resistive bridge network as a sensor of the diaphragm deformation resulting from the external pressures encountered. Because of the limited circumferential extent, information regarding the luminar pressures at a location may be incomplete. Additionally, electrical conductors must extend through the catheter system to each sensor element, creating a potential safety issue, as well as limiting the number of sensor elements because of the finite space available to route the many conductors through the central catheter lumen. In the water-perfused system, small tubes, one for each sensed location, must be contained in a larger lumen, and each tube terminated at the sensed location by a hole in the outer lumen wall. This hole is also of a very limited circumferential extent, and a large number of sensor locations require an increasing diameter of the outer lumen. This ultimately limits the practical number of sensors that can be accommodated. The fluid path(s) also present an electrically conductive path, which also contributes to safety concerns.
Requirements for the spatial density of recording sensors will undoubtedly vary across tubular organs in the body. Presently, the gastrointestinal tract is an important organ system with clinically relevant motility disorders, and, within that system, the most studied tubular organ for its motor function is the esophagus. Through a series of reports from 1991-2000, Clouse demonstrated that complete characterization of the esophageal peristaltic sequence would require 1-cm sensor spacing; including appropriate oropharyngeal and gastric sensors to fulfill measurement requirements, thirty-two simultaneous intraluminal pressure measurement are needed. Adding a requirement that the sensors have sensitivity to pressures over a significant circumferential extent would improve the completeness of the measurement at each sensor location. Employing fiber-optic techniques to sense the deformation of the segment would eliminate any electrical safety concern, as no electrically conductive path would exist.
Modern desktop computers can acquire, store and process large quantities of data obtained from multivariate sources and acquisition of data from sixty-four data channels with sixteen-bit resolution and at speeds greater than 100 kilosamples per second is possible today. Processor speeds approaching a billion operations per second, on-board storage of several hundred million bytes of information, and high speed mass storage devices capable if tens of billion bytes of information are now in existence. With these capabilities, very sophisticated signal processing operations such as data averaging, filtering and engineering unit conversion can be accomplished in virtually real-time. Elaborate graphical displays of multivariate dataxe2x80x94xe2x80x9cwaterfall diagramsxe2x80x9d, xe2x80x9cmesh diagramsxe2x80x9d, xe2x80x9ccontour plotsxe2x80x9d, and xe2x80x9ccontour plots employing xe2x80x9cpseudo-colorsxe2x80x9dxe2x80x94are encountered in many fields, computational fluid dynamics, seismology, and target identification and tracking to name a few. Of relevance to this disclosure is display of the space-time-amplitude distribution of the bodily pressures being exerted along any of several tubular cavities within the body. Classification of the medical conditions implicit in these complex sets of data has been performed by experts in the field who have access to systems that can acquire the requisite data. At the present time, interpretation of a given set of data may result in inconsistencies because of different medical training, experience, stress level, etc.; or one physician""s mental rules may be difficult to articulate and thus difficult to transfer to others; or where the patient""s condition is overly complex and not well understood. Some of these inconsistencies may be eliminated or reduced through the application of computer aided diagnostic routines based on some form of artificial intelligence (AI) technology. In this context, AI is deemed to be the use of advanced computing techniques for performing tasks usually considered to require human insight or intervention. AI includes many advanced computational techniques including expert systems, artificial neural networks, fuzzy logic, and genetic algorithms. Expert systems are rule-based systems where the rules are based on expert decisions or on historical data. One usually describes these routines as a compilation of IF-THEN statements. Fuzzy logic allows for some relaxation of the rules by defining a percentage membership in a set. In genetic algorithms, varying each of a problem""s parameters over the allowable ranges generates a population of random potential solutions. An xe2x80x9cobjectivexe2x80x9d function then rates each member of the population. New individuals are then generated by combining the parameters of two random members of the population (mixing genes) or by randomly varying one or more parametric values of an existing population member (mutation). When a new member is generated, it is compared with the weakest member of the population. If it is stronger than the weakest member, it assumes a place in the population and the weakest member is discarded. The process continues until little further improvement is noted. The fittest member is then regarded as the optimized solution. Artificial neural networks are self-optimizing predictive programs that are useful when historical data on system performance is available. Unlike expert systems, where predictive or analytical rules are usually derived explicitly, neural networks learn through repeated examination of sample cases. Data is presented to a network-training program in the form of training sets, which consist of input data (such as the result of a set of medical tests) and output or results (a validated diagnosis of the patient""s condition). When the network has completed its training on the supplied historic data, it can be used to predict cases upon which it has not been trained, provided the situation to be predicted is reasonably similar to the training cases.
It is the primary object of this invention to provide a system and method that acquires, graphically displays, and analytically interprets the space-time pressure distributions within a bodily cavity or lumen. To achieve this objective, the system includes: (1) a catheter made up of a flexible support structure with multiple transducer segments, each sensitive to externally applied, circumferential pressures, discretely located along its length; (2) a signal conditioning sub-system to provide an electrical analog of the applied pressure from each measuring segment; (3) a data acquisition unit where the raw analog data from each segment is acquired, normalized, converted to engineering units, and stored so that further data processing might be performed; (4) any of several data processing routines such as averaging, windowing, correlation analysis, and the like; (5) a data plotting module where various data visualization presentations are constructed, such as amplitude vs. time plots for discrete segments, 3-D mesh or waterfall plots to visualize the amplitude-space-time relationships, and/or space-time relationships with amplitude expressed by contours or pseudocolor; (6) and finally, an interpretive module that, once trained, identifies the most probable dysfunction characterized by that data set.
Up to the present time, clinical studies alluded to herein have been conducted by experts in facilities conducting research or in facilities specializing in a particular physiological dysfunction, which obviated the need for more inclusive systems. Multiple sensors to adequately characterize the bodily structure of interest from a single forcing function and sufficiently powerful desk top computer systems and data acquisition capabilities to acquire, process and display the acquired data sequence in near real-time are now available. Adding built-in diagnostic routines to interpret the acquired data patterns and identify the most probable dysfunction, allows the present system to be utilized by less skilled practitioners. Obtaining, displaying, and interpreting a sufficiency of data in a minimum of time will minimize the discomfort to the patient, reduce the cost of patient care, and greatly increase the number of facilities where comparable investigations can be performed. Also, because the data is now in a standardized form, it is easily transmitted electronically to a specialist for additional consultation.